The present invention relates to aerial refueling, and more particularly relates to improved system, apparatus and methods for controlling the slack in the refueling hose during the refueling operation.
The process of aerial refueling is well known and allows a plane or other aircraft to be refueled in flight without the need to land. This is typically used by the military for long distance flights where landing of the air craft would be impossible, unsafe or otherwise undesirable. The refueling process consists of a leading aircraft which refuels a trailing aircraft via a rigid boom or flexible hose that typically includes a funnel-shaped device (referred to as a “drogue”) at the free end thereof which releasably engages with a probe leading to the fuel tank of the trailing aircraft. With the leading aircraft travelling at a constant speed and the hose/drogue freely extending therebehind, the trailing aircraft probe is aligned with the drogue and its speed is increased in an attempt to couple the probe and drogue. This maneuver is typically called “making a run at the drogue”. Sometimes the alignment is off and the coupling fails whereupon the sequence is repeated until a successful coupling has occurred. When the drogue and probe are coupled, fuel may be delivered from an auxiliary fuel tank on the leading aircraft through the boom or hose to the probe of the trailing aircraft which leads to the trailing aircraft fuel tank(s), thereby refueling the trailing aircraft during flight.
One potential problem that occurs in such a refueling system is controlling the slack and oscillations in the flexible hose. If there is too much slack in the hose when the drogue and probe are in the coupling process or after they are coupled, this can cause the hose to oscillate and fail to couple or unintentionally detach from the probe.
The following patents illustrate various attempts to control the above hose slack problem in aerial refueling systems:    U.S. Pat. No. 6,454,212 issued to Bartov on Sep. 24, 2002    U.S. Pat. No. 6,786,455 issued to Bartov on Sep. 7, 2004    U.S. Pat. No. 6,866,228 issued to Bartov on Mar. 15, 2005
The '212 patent utilizes a reaction torque sensor and microprocessor which connects to the control valve of a variable displacement hydraulic motor which controls the deployment and retraction of the hose reel. The microprocessor receives data relating to the reaction torque on the hose reel (i.e., as a result of contact of the receiving aircraft's refueling probe with the drogue and/or air stream effects) from the reaction torque sensor 36 which is preferably a load cell electrically connected to the microprocessor. The microprocessor also receives data on the position (speed and direction) of the hose from a tachometer/position sensor 34 which is preferably connected to the drive shaft of the hose reel to measure how much length and how fast the hose is deploying from the reel. The microprocessor then sends signals to the hydraulic motor control valve in response to the signals it receives from the command instructions initiated by the tanker aircraft's pilot or by avionic equipment (e.g., deploy or retract hose), as well as the tachometer/position sensor and torque sensor. Thus, the hose is controlled in this instance by sensing the position and speed of the hose as it leaves the reel, and the torque on the reel as caused by forces acting on the drogue by the probe and/or air currents. The free drag torque is compared to the net drag torque and signals are generated and sent to the control valve according to the microprocessor algorithm. As explained at Column 6, lines 50-65 of the '212 patent, if the net drag torque drops too far below the free drag torque, dangerous slack may develop in the hose. The algorithm thus calculates the net drag force and reacts to a predetermined threshold reading by sending a signal to retract the hose.
The '228 patent, which is a continuation-in-part of the '212 patent, discloses the further step of retracting the hose prior to hook-up with the probe to record the free hose retraction force which is then compared to the retraction force following engagement with retraction continuing until the retraction force rises to about the same force as previously recorded.
The '455 patent discloses drogue and probe positors (position sensors, transmitters and/or receivers) which are capable of determining the relative positions of the drogue and probe. Once the probe and drogue are in orthogonal alignment, the hose is extended further to reach and engage the probe (this is opposed to the trailing aircraft making a run at the drogue which the inventor states can cause slack in the hose). Air jets (thrusters) about the drogue may also be used to assist in the alignment of the probe and drogue.
Although the above patents illustrate various methods and systems by which a refueling hose may be monitored and controlled during the refueling operation, there still remains a need for a more precise system and method of controlling slack in the refueling hose by utilizing the coupling event between the probe and drogue as a system control parameter.